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package javax.xml.xpath;

import org.xml.sax.InputSource;
import javax.xml.namespace.QName;

/**
 * <p><code>XPathExpression</code> provides access to compiled XPath expressions.</p>
 *
 * <a name="XPathExpression-evaluation"/> <table border="1" cellpadding="2"> <thead> <tr> <th
 * colspan="2">Evaluation of XPath Expressions.</th> </tr> </thead> <tbody> <tr> <td>context</td>
 * <td> If a request is made to evaluate the expression in the absence of a context item, an empty
 * document node will be used for the context. For the purposes of evaluating XPath expressions, a
 * DocumentFragment is treated like a Document node. </td> </tr> <tr> <td>variables</td> <td> If the
 * expression contains a variable reference, its value will be found through the {@link
 * XPathVariableResolver}. An {@link XPathExpressionException} is raised if the variable resolver is
 * undefined or the resolver returns <code>null</code> for the variable. The value of a variable
 * must be immutable through the course of any single evaluation.</p> </td> </tr> <tr>
 * <td>functions</td> <td> If the expression contains a function reference, the function will be
 * found through the {@link XPathFunctionResolver}. An {@link XPathExpressionException} is raised if
 * the function resolver is undefined or the function resolver returns <code>null</code> for the
 * function.</p> </td> </tr> <tr> <td>QNames</td> <td> QNames in the expression are resolved against
 * the XPath namespace context. </td> </tr> <tr> <td>result</td> <td> This result of evaluating an
 * expression is converted to an instance of the desired return type. Valid return types are defined
 * in {@link XPathConstants}. Conversion to the return type follows XPath conversion rules.</p>
 * </td> </tr> </table>
 *
 * <p>An XPath expression is not thread-safe and not reentrant. In other words, it is the
 * application's responsibility to make sure that one {@link XPathExpression} object is not used
 * from more than one thread at any given time, and while the <code>evaluate</code> method is
 * invoked, applications may not recursively call the <code>evaluate</code> method. <p>
 *
 * @author <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a>
 * @author <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>
 * @see <a href="http://www.w3.org/TR/xpath#section-Expressions">XML Path Language (XPath) Version
 * 1.0, Expressions</a>
 * @since 1.5
 */
public interface XPathExpression {

  /**
   * <p>Evaluate the compiled XPath expression in the specified context and return the result as the
   * specified type.</p>
   *
   * <p>See <a href="#XPathExpression-evaluation">Evaluation of XPath Expressions</a> for context
   * item evaluation, variable, function and QName resolution and return type conversion.</p>
   *
   * <p>If <code>returnType</code> is not one of the types defined in {@link XPathConstants}, then
   * an <code>IllegalArgumentException</code> is thrown.</p>
   *
   * <p>If a <code>null</code> value is provided for <code>item</code>, an empty document will be
   * used for the context. If <code>returnType</code> is <code>null</code>, then a
   * <code>NullPointerException</code> is thrown.</p>
   *
   * @param item The starting context (a node, for example).
   * @param returnType The desired return type.
   * @return The <code>Object</code> that is the result of evaluating the expression and converting
   * the result to <code>returnType</code>.
   * @throws XPathExpressionException If the expression cannot be evaluated.
   * @throws IllegalArgumentException If <code>returnType</code> is not one of the types defined in
   * {@link XPathConstants}.
   * @throws NullPointerException If  <code>returnType</code> is <code>null</code>.
   */
  public Object evaluate(Object item, QName returnType)
      throws XPathExpressionException;

  /**
   * <p>Evaluate the compiled XPath expression in the specified context and return the result as a
   * <code>String</code>.</p>
   *
   * <p>This method calls {@link #evaluate(Object item, QName returnType)} with a
   * <code>returnType</code> of {@link XPathConstants#STRING}.</p>
   *
   * <p>See <a href="#XPathExpression-evaluation">Evaluation of XPath Expressions</a> for context
   * item evaluation, variable, function and QName resolution and return type conversion.</p>
   *
   * <p>If a <code>null</code> value is provided for <code>item</code>, an empty document will be
   * used for the context.
   *
   * @param item The starting context (a node, for example).
   * @return The <code>String</code> that is the result of evaluating the expression and converting
   * the result to a <code>String</code>.
   * @throws XPathExpressionException If the expression cannot be evaluated.
   */
  public String evaluate(Object item)
      throws XPathExpressionException;

  /**
   * <p>Evaluate the compiled XPath expression in the context of the specified
   * <code>InputSource</code> and return the result as the specified type.</p>
   *
   * <p>This method builds a data model for the {@link InputSource} and calls {@link
   * #evaluate(Object item, QName returnType)} on the resulting document object.</p>
   *
   * <p>See <a href="#XPathExpression-evaluation">Evaluation of XPath Expressions</a> for context
   * item evaluation, variable, function and QName resolution and return type conversion.</p>
   *
   * <p>If <code>returnType</code> is not one of the types defined in {@link XPathConstants}, then
   * an <code>IllegalArgumentException</code> is thrown.</p>
   *
   * <p>If <code>source</code> or <code>returnType</code> is <code>null</code>, then a
   * <code>NullPointerException</code> is thrown.</p>
   *
   * @param source The <code>InputSource</code> of the document to evaluate over.
   * @param returnType The desired return type.
   * @return The <code>Object</code> that is the result of evaluating the expression and converting
   * the result to <code>returnType</code>.
   * @throws XPathExpressionException If the expression cannot be evaluated.
   * @throws IllegalArgumentException If <code>returnType</code> is not one of the types defined in
   * {@link XPathConstants}.
   * @throws NullPointerException If  <code>source</code> or <code>returnType</code> is
   * <code>null</code>.
   */
  public Object evaluate(InputSource source, QName returnType)
      throws XPathExpressionException;

  /**
   * <p>Evaluate the compiled XPath expression in the context of the specified
   * <code>InputSource</code> and return the result as a <code>String</code>.</p>
   *
   * <p>This method calls {@link #evaluate(InputSource source, QName returnType)} with a
   * <code>returnType</code> of {@link XPathConstants#STRING}.</p>
   *
   * <p>See <a href="#XPathExpression-evaluation">Evaluation of XPath Expressions</a> for context
   * item evaluation, variable, function and QName resolution and return type conversion.</p>
   *
   * <p>If <code>source</code> is <code>null</code>, then a <code>NullPointerException</code> is
   * thrown.</p>
   *
   * @param source The <code>InputSource</code> of the document to evaluate over.
   * @return The <code>String</code> that is the result of evaluating the expression and converting
   * the result to a <code>String</code>.
   * @throws XPathExpressionException If the expression cannot be evaluated.
   * @throws NullPointerException If  <code>source</code> is <code>null</code>.
   */
  public String evaluate(InputSource source)
      throws XPathExpressionException;
}
